Drive device and image forming apparatus incorporating the drive device

ABSTRACT

A drive device, which is incorporated in an image forming apparatus, includes a drive motor and a plurality of gears driven by the drive motor. The plurality of gears include at least two gears disposed coaxially with each other and have a plurality of meshing portions. Each meshing portion is formed between a pair of gears of the plurality of gears. A difference between respective gear mesh frequencies of the plurality of meshing portions is set equal to or smaller than 100 Hz.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of and claims priority under35 U.S.C. §§ 120/121 to U.S. application Ser. No. 15/088,540 filed onApr. 1, 2016, which is based on and claims priority pursuant to 35U.S.C. § 119(a) to Japanese Patent Application No. 2015-075936, filed onApr. 2, 2015, in the Japan Patent Office, the entire disclosures of eachof which are hereby incorporated by reference herein.

BACKGROUND Technical Field

This disclosure relates to a drive device and an image forming apparatusincorporating the drive device.

Related Art

Various types of image forming apparatuses include copiers, printers,facsimile machine, or multifunction peripherals (MFPs) having two ormore of copying, printing, scanning, facsimile transmission, plotter,and other capabilities. Such image forming apparatuses include multipledrive devices for image formation. The multiple drive devices are usedfor operations of a photoconductor and a transfer belt.

For example, a known drive device includes a motor that includes a motorgear, an internal gear that meshes with the motor gear, an external gearthat is coaxially mounted with the internal gear and rotates togetherwith the internal gear, and an output gear that meshes with the externalgear and outputs a driving force to a drive transmission object.

SUMMARY

At least one aspect of this disclosure provides a drive device includinga drive motor and a plurality of gears driven by the drive motor. Theplurality of gears include at least two gears disposed coaxially witheach other and has a plurality of meshing portions. Each meshing portionis formed between a pair of gears of the plurality of gears. Adifference between respective gear mesh frequencies of the plurality ofmeshing portions is set equal to or smaller than 100 Hz.

Further, at least one aspect of this disclosure provides an imageforming apparatus including the above-described drive device and animage forming device to receive a driving force transmitted from thedrive device.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic view illustrating an image forming apparatusaccording to an embodiment of this disclosure;

FIG. 2 is a schematic view illustrating a process unit included in theimage forming apparatus of FIG. 1;

FIG. 3 is a schematic cross sectional view illustrating a drive deviceincluded in the image forming apparatus of FIG. 1;

FIG. 4 is a graph of relation of sound pressure level and frequency ofsound emitted when a comparative drive device is driven;

FIG. 5 is a schematic cross sectional view illustrating the comparativedrive device in which an internal gear is used as an idler gear;

FIG. 6A is a graph illustrating the effect of sound absorption by usingHelmholtz sound absorber;

FIG. 6B is a graph illustrating another effect of sound absorption byusing Helmholtz sound absorber;

FIG. 7 is a schematic cross sectional view illustrating a drive deviceof Variation 1;

FIG. 8 is a schematic cross sectional view illustrating a drive deviceof Variation 2;

FIG. 9 is a schematic cross sectional view illustrating a drive deviceof Variation 3;

FIG. 10 is a schematic cross sectional view illustrating a drive deviceof Variation 4;

FIG. 11 is a schematic cross sectional view illustrating an example ofnoise reduction measures;

FIG. 12 is a schematic cross sectional view illustrating another exampleof noise reduction measures;

FIG. 13 is a perspective view illustrating a motor sound absorber; and

FIG. 14 is a schematic cross sectional view illustrating yet anotherexample of noise reduction measures.

DETAILED DESCRIPTION

It will be understood that if an element or layer is referred to asbeing “on”, “against”, “connected to” or “coupled to” another element orlayer, then it can be directly on, against, connected or coupled to theother element or layer, or intervening elements or layers may bepresent. In contrast, if an element is referred to as being “directlyon”, “directly connected to” or “directly coupled to” another element orlayer, then there are no intervening elements or layers present. Likenumbers referred to like elements throughout. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

Spatially relative terms, such as “beneath”, “below”, “lower”, “above”,“upper” and the like may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements describes as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, term such as “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors herein interpreted accordingly.

Although the terms first, second, etc. may be used herein to describevarious elements, components, regions, layers and/or sections, it shouldbe understood that these elements, components, regions, layer and/orsections should not be limited by these terms. These terms are used todistinguish one element, component, region, layer or section fromanother region, layer or section. Thus, a first element, component,region, layer or section discussed below could be termed a secondelement, component, region, layer or section without departing from theteachings of the present disclosure.

The terminology used herein is for describing particular embodiments andexamples and is not intended to be limiting of exemplary embodiments ofthis disclosure. As used herein, the singular forms “a”, “an” and “the”are intended to include the plural forms as well, unless the contextclearly indicates otherwise. It will be further understood that theterms “includes” and/or “including”, when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof.

Descriptions are given, with reference to the accompanying drawings, ofexamples, exemplary embodiments, modification of exemplary embodiments,etc., of an image forming apparatus according to exemplary embodimentsof this disclosure. Elements having the same functions and shapes aredenoted by the same reference numerals throughout the specification andredundant descriptions are omitted. Elements that do not demanddescriptions may be omitted from the drawings as a matter ofconvenience. Reference numerals of elements extracted from the patentpublications are in parentheses so as to be distinguished from those ofexemplary embodiments of this disclosure.

This disclosure is applicable to any image forming apparatus, and isimplemented in the most effective manner in an electrophotographic imageforming apparatus.

In describing preferred embodiments illustrated in the drawings,specific terminology is employed for the sake of clarity. However, thedisclosure of this disclosure is not intended to be limited to thespecific terminology so selected and it is to be understood that eachspecific element includes any and all technical equivalents that havethe same function, operate in a similar manner, and achieve a similarresult.

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views, preferredembodiments of this disclosure are described.

Now, a description is given of an electrophotographic image formingapparatus 100 for forming images by electrophotography, according to anembodiment of this disclosure. It is to be noted that, hereinafter, theelectrophotographic image forming apparatus 100 is referred to as theimage forming apparatus 100.

At first, a description is given of a basic configuration of the imageforming apparatus 100 according to the present embodiment of thisdisclosure.

FIG. 1 is a schematic view illustrating an image forming apparatus 100according to the present embodiment of this disclosure. The imageforming apparatus 100 includes four process units 26K, 26C, 26M, and 26Yto form respective toner images of black (K), cyan (C), magenta (M), andyellow (Y). The configurations of the process units 26K, 26C, 26M, and26Y are basically identical to each other, except that the process units26K, 26C, 26M, and 26Y include toners of different colors. Each of theprocess units 26K, 26C, 26M, and 26Y is replaced at the end of itsservice life.

It is to be noted that identical parts are given identical referencenumerals and redundant descriptions are summarized or omittedaccordingly.

The image forming apparatus 100 may be a copier, a facsimile machine, aprinter, a multifunction peripheral or a multifunction printer (MFP)having at least one of copying, printing, scanning, facsimile, andplotter functions, or the like. According to the present example, theimage forming apparatus 100 is an electrophotographic copier that formstoner images on recording media by electrophotography.

It is to be noted in the following examples that: the term “imageforming apparatus” indicates an apparatus in which an image is formed ona recording medium such as paper, OHP (overhead projector)transparencies, OHP film sheet, thread, fiber, fabric, leather, metal,plastic, glass, wood, and/or ceramic by attracting developer or inkthereto; the term “image formation” indicates an action for providing(i.e., printing) not only an image having meanings such as texts andfigures on a recording medium but also an image having no meaning suchas patterns on a recording medium; and the term “sheet” is not limitedto indicate a paper material but also includes the above-describedplastic material (e.g., a OHP sheet), a fabric sheet and so forth, andis used to which the developer or ink is attracted. In addition, the“sheet” is not limited to a flexible sheet but is applicable to a rigidplate-shaped sheet and a relatively thick sheet.

Further, size (dimension), material, shape, and relative positions usedto describe each of the components and units are examples, and the scopeof this disclosure is not limited thereto unless otherwise specified.

Further, it is to be noted in the following examples that: the term“sheet conveying direction” indicates a direction in which a recordingmedium travels from an upstream side of a sheet conveying path to adownstream side thereof; the term “width direction” indicates adirection basically perpendicular to the sheet conveying direction.

FIG. 2 is a schematic view illustrating one of the process units 26K,26C, 26M, and 26Y.

Since the process units 26K, 26C, 26M, and 26Y have respectiveconfigurations identical to each other except the toner colors, theprocess unit 26 and image forming components included in the processunit 26 are described without suffixes indicating the toner colors,which are K, C, M, and Y.

As illustrated in FIG. 2, the process unit 26 includes a photoconductorunit 10 and a developing unit 23. The photoconductor unit 10 supports adrum-shaped photoconductor 24 that functions as an image bearer, aphotoconductor cleaning device 83, a static eliminating device, and acharging device 25. The process unit 26 is detachably attachable to anapparatus body of the image forming apparatus 100, and consumable partsof the process unit 26 can be replaced at one time.

The charging device 25 uniformly charges a surface of the photoconductor24 that is rotated by a drive unit in a clockwise direction in FIG. 2.An optical writing unit 27 emits a laser light beam L so as to irradiatethe uniformly charged surface of the photoconductor 24 to form anelectrostatic latent image of each single color toner. The developingunit 23 incorporating toner develops the electrostatic latent image intoa toner image. Then, the toner image is primarily transferred onto asurface of an intermediate transfer belt 22.

The photoconductor cleaning device 83 removes residual toner remainingon the surface of the photoconductor 24 after a primary transferoperation. Further, the static eliminating device removes residualelectric potential remaining on the surface of the photoconductor 2after the photoconductor cleaning device 83 has cleaned the surface ofthe photoconductor 24. This removal of static electricity initializesthe surface of the photoconductor 24, so as to prepare for a subsequentimage formation.

The developing unit 23 includes a hopper 86 and a developing section 87.The hopper 86 is a vertically long member to contain toner thatfunctions as developer. The hopper 86 that functions as a developercontainer includes an agitator 88 and a toner supply roller 80. Theagitator 88 is rotated by the drive unit. The toner supply roller 80that functions as a developer supplier is disposed at a portionvertically lower from the agitator 88 and is rotated by the drive unit.Toner contained in the hopper 86 moves toward the toner supply roller 80by the force of gravity while being agitated due to rotation of theagitator 88. The toner supply roller 80 includes a metallic cored barand a roller including foam resin covering a surface of the metalliccored bar. The toner supply roller 80 rotates while collecting the toneraccumulated at a lower part of the hopper 86 to the surface of the tonersupply roller 80.

The developing section 87 of the developing unit 23 includes adeveloping roller 81 and a thin layer forming blade 82. The developingroller 81 rotates while contacting the photoconductor 24 and the tonersupply roller 80. The thin layer forming blade 82 has a leading edge tocontact a surface of the developing roller 81. The toner adhering to thetoner supply roller 80 in the hopper 86 is supplied to the surface ofthe developing roller 81 at a contact portion at which the developingroller 81 and the toner supply roller 80 contact each other. The tonersupplied onto the surface of the developing roller 81 passes the contactposition at which the developing roller 81 and the thin layer formingblade 82 contact each other along with rotation of the developing roller81. At this time, the thickness of layer of toner on the surface of thedeveloping roller 81 is regulated. After the thickness of layer isregulated, the toner adheres to the electrostatic latent image formed onthe surface of the photoconductor 24 in a development region thatcorresponds to a contact portion of the developing roller 81 and thephotoconductor 24. This adhesion of toner develops the electrostaticlatent image into a visible toner image.

Such toner image formation is performed in each process unit 26 (i.e.,the process units 26K, 26C, 26M, and 26Y), so that a single color tonerimage of each process unit 26 is formed on the surface of thephotoconductor 24 (i.e., the photoconductors 24K, 24C, 24M, and 24Y).

As illustrated in FIG. 1, an optical writing unit 27 is disposedvertically above the process units 26K, 26C, 26M, and 26Y. The opticalwriting unit 27 functions as a latent image writing device. The opticalwriting unit 27 emits laser light L from a laser diode based on imagedata to optically scan the photoconductors 24K, 24C, 24M, and 24Y in theprocess units 26K, 26C, 26M, and 26Y, respectively. Due to this opticalscanning, an electrostatic latent image is formed on the surface of eachphotoconductor 24. In this configuration, the optical writing unit 27and the four process units 26K, 26C, 26M, and 26Y form an image formingdevice that forms respective black, cyan, magenta, and yellow tonerimages, which are visible images of different colors from each other, onthe photoconductors 24K, 24C, 24M, and 24Y.

While causing a polygon motor to rotate a polygon mirror so as todeflect the laser light L emitted by the light source in a main scanningdirection, the optical writing unit 27 irradiates the deflected laserlight L to the photoconductor 24 via multiple optical lenses andmirrors. The optical writing unit 27 may be a device that performsoptical writing by LED light emitted by multiple light emitting diodes(LEDs) of an LED array.

A transfer unit 75 is disposed vertically below the photoconductors 24K,24C, 24M, and 24Y. The transfer unit 75 functions as a belt unit thatrotates endlessly in a counterclockwise direction in FIG. 1 whilestretching the endless intermediate transfer belt 22 with tension. Thetransfer unit 75 includes the intermediate transfer belt 22, a driveroller 76, a tension roller 20, four primary transfer rollers 74K, 74C,74M, and 74Y, a secondary transfer roller 21, a belt cleaning device 71,and a cleaning backup roller 72.

The intermediate transfer belt 22 functions as a belt member as well asa transfer roller. The intermediate transfer belt 22 is stretched by thedrive roller 76, the tension roller 20, the cleaning backup roller 72,and the four primary transfer rollers 74K, 74C, 74M, and 74Y, which aredisposed inside the loop of the intermediate transfer belt 22. Then, dueto a rotation force of the drive roller 76 that is rotated by a driveunit in the counterclockwise direction in FIG. 1, the intermediatetransfer belt 22 is endlessly rotated in the same direction as the driveroller 76.

The four primary transfer rollers 74K, 74C, 74M, and 74Y hold theintermediate transfer belt 22 that rotates endlessly with thephotoconductors 24K, 24C, 24M, and 24Y. By so doing, four primarytransfer nip regions are formed on respective four positions where afront face of the intermediate transfer belt 22 and respectivephotoconductors 24K, 24C, 24M, and 24Y contact.

Primary transfer biases are applied by a transfer power supply to theprimary transfer rollers 74K, 74C, 74M, and 74Y, respectively.Accordingly, a transfer electric field is formed in each transfer nipregion formed between the electrostatic latent image of thephotoconductor 24 (i.e., the photoconductors 24K, 24C, 24M, and 24Y) andthe primary transfer roller 74 (i.e., the primary transfer rollers 74K,74C, 74M, and 74Y). It is to be noted that the primary transfer roller74 may be replaced with a transfer charger or a transfer brush.

The yellow toner image formed on the surface of the photoconductor 24Yof the process unit 26Y enters the primary transfer nip region as thephotoconductor 24Y rotates. In the primary transfer nip region foryellow toner image, due to the transfer electric field and a nippressure, the yellow toner image is primarily transferred from thephotoconductor 24Y onto the intermediate transfer belt 22. After theyellow toner image is primarily transferred onto the intermediatetransfer belt 22, the intermediate transfer belt 22 continues to rotateendlessly. As the intermediate transfer belt 22 rotates and passes theprimary transfer nip regions for magenta, cyan, and black toner images,the magenta, cyan, and black toner images formed on the photoconductors24M, 24C, and 24K are also primarily transferred and sequentiallyoverlaid onto the intermediate transfer belt 22. By primarilytransferring the single color toner images, a four-color toner image isformed on the intermediate transfer belt 22.

The secondary transfer roller 21 included in the transfer unit 75 isdisposed outside the loop of the intermediate transfer belt 22 to holdthe intermediate transfer belt 22 with the tension roller 20 disposedinside the loop of the intermediate transfer belt 22. By so doing, asecondary transfer nip region is formed between a front face of theintermediate transfer belt 22 and the secondary transfer roller 21. Asecondary transfer bias is applied by the transfer bias power supply tothe secondary transfer roller 21. This application of the secondarytransfer bias forms a secondary transfer electric field between thesecondary transfer roller 21 and the tension roller 20 that iselectrically grounded.

A sheet tray 41 is disposed vertically below the transfer unit 75. Thesheet tray 41 accommodates multiple recording media in a bundle ofsheets. The sheet tray 41 is slidably and detachably attached to anapparatus body of the image forming apparatus 100. The sheet tray 41includes a feed roller 42 that is disposed in contact with a recordingmedium that is placed on top of the bundle of sheets. As the feed roller42 rotates in the counterclockwise direction in FIG. 1 at apredetermined timing, the recording medium is fed toward a sheetconveying path.

A pair of registration rollers 42 is disposed at a far end of the sheetconveying path. The pair of registration rollers 43 includes tworegistration rollers. The pair of registration rollers 43 stops rotatingat on receiving the recording medium fed from the sheet tray 41 betweenthe two registration rollers. In synchronization of arrival of thefour-color toner image formed on the intermediate transfer belt 22 inthe secondary transfer nip region, the pair of registration rollers 43starts rotating again to further convey the recording medium toward thesecondary transfer nip region.

When the four-color toner image formed on the intermediate transfer belt22 closely contacts the recording medium at the secondary transfer nipregion, the four-color toner image is transferred onto the recordingmedium due to the secondary transfer electric field and the nippressure. At this time, the four-color toner image is combined withwhite color of the recording medium to make a full-color toner image. Byso doing, the full-color toner image is formed on a front face of therecording medium. As the recording medium with the full-color tonerimage on the front face passes the secondary transfer nip region, therecording medium separates from the secondary transfer roller 21 and theintermediate transfer belt 22 due to curvature separation. Then, therecording medium travels through a post-transfer conveying path andreaches a fixing device 40.

After passing through the secondary transfer nip region, residual tonerthat has not been transferred onto the recording medium remains on theintermediate transfer belt 22. The residual toner remaining on thesurface of the intermediate transfer belt 22 is removed by the beltcleaning device 71 that is disposed in contact with the surface of theintermediate transfer belt 22. The residual toner remaining on thesurface of the intermediate transfer belt 22 is removed by the beltcleaning device 71 that is disposed in contact with the surface of theintermediate transfer belt 22.

The fixing device 40 includes a fixing roller 45 and a pressure roller47. The fixing roller 45 includes a heat generating source 45 a such asa halogen lamp. The pressure roller 47 rotates while pressing againstthe fixing roller 45 with a predetermined pressing force. The fixingroller 45 and the pressure roller 47 contact each other to form a fixingnip region. The recording medium conveyed to the fixing device 40 isheld in the fixing nip region such that a face on which an unfixed tonerimage is formed contacts the fixing roller 45. Then, toner in theunfixed toner image melts by application of heat and pressure, so thatthe full-color toner image is fixed to the recording medium.

In a single side printing mode, the recording medium discharged from thefixing device 40 is ejected to an outside of the image forming apparatus100. Then, the recording medium is stored on a sheet stacking portionthat is constructed by an upper face of a top cover 56 of the apparatusbody of the image forming apparatus 100.

The top cover 56 of the apparatus body of the image forming apparatus100 is rotatably supported by a top cover shaft 51 as indicated by arrowA in FIG. 1. By rotating in the counterclockwise direction in FIG. 1,the top cover 56 opens from the apparatus body of the image formingapparatus 100. Then, an upper opening of the apparatus body of the imageforming apparatus 100 is widely exposed. In addition, the opticalwriting unit 27 is also rotatably supported by the top cover shaft 51.By rotating the optical writing unit 27 in the counterclockwisedirection in FIG. 1, an upper face of the process units 26K, 26C, 26M,and 26Y is exposed.

The process units 26K, 26C, 26M, and 26Y are attached to and detachedfrom the apparatus body of the image forming apparatus 100 by openingthe top cover 56 and the optical writing unit 27. Specifically, byopening the top cover 56 and the optical writing unit 27, the upper faceof the process units 26K, 26C, 26M, and 26Y are exposed. Then, bypulling the process units 26K, 26C, 26M, and 26Y in a vertically upwarddirection, the process units 26K, 26C, 26M, and 26Y are removed andtaken out from the apparatus body of the image forming apparatus 100.

With this configuration, the process unit 26 that is frequently attachedto and detached from the apparatus body of the image forming apparatus100 is attached to and detached from the image forming apparatus 100 byopening the top cover 56 and the optical writing unit 27. Accordingly,attachment and detachment of the process unit 26 can be checked byallowing a user or an operator to do visual observation of the inside ofthe apparatus body of the image forming apparatus 100 from above withoutimposing difficult posture such as crouching, bending, and squatting onthe user or the operator. As a result, the workload of the user or theoperator can be reduce and occurrence of error in operation can beprevented.

It is to be noted that the photoconductor unit 10 and the developingunit 23 are included in the process unit 26 according to the presentembodiment, so that the photoconductor unit 10 and the developing unit23 are attached to and detached from the apparatus body of the imageforming apparatus 100 together. However, the configuration is notlimited thereto and the photoconductor unit 10 and the developing unit23 can be attached to and detached from the apparatus body of the imageforming apparatus 100 separately.

Next, a description is given of a drive device 110 according to thepresent embodiment of this disclosure.

FIG. 3 is a schematic cross sectional view illustrating the drive device110 that is included in the image forming apparatus 100 to drive adeveloping roller 81.

As illustrated in FIG. 3, the drive device 110 includes a driving motor111 and a reduction gear 116. The reduction gear 116 includes aninternal gear 116 a having internal teeth and an external gear 116 bhaving external teeth. The internal teeth of the internal gear 116 a aremeshed with teeth of a motor gear 111 a that is mounted on a motor shaftof the driving motor 111. Further, the external teeth of the externalgear 116 b are meshed with teeth of an output gear 118 that is mountedon a development driving shaft 81 a that is connected to a shaft of thedeveloping roller 81 via a joint.

The reduction gear 116 is rotatably supported by a support shaft 117that is secured by caulking by a first plate 112 and a second plate 113that is disposed facing the first plate 112. The development drivingshaft 81 a is rotatably supported by the second plate 113 via a bearing81 b. The driving motor 111 is attached to the first plate 112. Thefirst plate 112 is positioned to a positioning pin 115 that is mountedon the second plate 113.

In the present embodiment, an internal gear such as the internal gear116 a is employed as a gear meshing with the motor gear 111 a. Byemploying the internal gear, a contact ratio of the internal gear andthe motor gear 111 a increases, and therefore vibration and noiseproduced by gear operation can be restrained. Further, a meshing portionwhere the internal gear 116 a and the motor gear 111 a mesh with eachother can be covered by the internal gear 116 a, and therefore meshingnoise of the internal gear 116 a and the motor gear 111 a can beblocked. The internal gear 116 a is shaped like a cylinder and one sideclose to the motor (hereinafter, a motor side) is open. Therefore,meshing noise is heard from an opening of the internal gear 116 a. Inthe present embodiment, however, the first plate 112 is disposed facingthe opening of the internal gear 116 a. Therefore, the meshing noise canbe prevented from being heard outside the drive device 110 from thefirst plate 112.

The reduction gear 116 according to the present embodiment furtherincludes reinforcing projections 116 c, an attaching portion 116 d, anda connecting portion 116 e. The reinforcing projections 116 c reinforcethe internal gear 116 a having a cylindrical shape. The support shaft117 passes through the attaching portion 116 d. The disk-shapedconnecting portion 116 e extends in a direction perpendicular to anaxial direction of the support shaft 117. In the present embodiment, theinternal gear 116 a and the attaching portion 116 d are connected viathe connecting portion 116 e. The reinforcing projections 116 c aredisposed on the connecting portion 116 e to reinforce the connectingportion 116 e. If the connecting portion 116 e is deformed, the meshingof the internal gear 116 a and the motor gear 111 a is changed. Thechange of the meshing of the internal gear 116 a and the motor gear 111a is likely to generate abnormal meshing vibration and abnormal wear oftooth. However, in the present embodiment, since the connecting portion116 e in the present embodiment is reinforced by the reinforcingprojections 116 c, deformation of the connecting portion 116 e can beprevented. Therefore, the meshing vibration and the abnormal wear oftooth can be prevented. Consequently, occurrence of defect image such asbanding due to meshing vibration can be prevented, and therefore highquality image can be maintained.

A driving force of the driving motor 111 is transmitted to the internalgear 116 a via the motor gear 111 a of the motor shaft. Then, thedriving force is further transmitted to the output gear 118 that ismeshed with the external gear 116 b of the reduction gear 116. Thedriving force is further transmitted to the developing roller 81 via thedevelopment driving shaft 81 a to rotate the developing roller 81 thatfunctions as a drive transmission object.

In a case in which multiple gears are used to transmit a driving force,vibration of gear mesh frequency at the meshing portion of gears inmesh. The vibration causes the driving motor 111, a first plate 112, anda second plate 113 to vibrate, resulting in generation of noise. Inorder to eliminate noise, Helmholtz sound absorbers are disposed aroundthe drive device 110, for example (see FIG. 11).

In another case in which vibration at the meshing portion is transmittedto the optical writing unit 27, for example, optical components andunits in the optical writing unit 27 resonate to form a defect imagesuch as banding. In order to eliminate such a defect image, the rigidityof optical components and units of the optical writing unit 27 ischanged to prevent the optical components and units from resonating.

As another example, respective rigidities of the first plate 112, thesecond plate 113, and the driving motor 111 are increased to make theresonance frequencies of the first plate 112, the second plate 113, andthe driving motor 111 different from the gear mesh frequency. By sodoing, vibration of the first plate 112, the second plate 113, and thedriving motor can be restrained. Accordingly, noise generated due tovibration of the first plate 112, the second plate 113, and the drivingmotor 111 can be restrained. Further, the configuration can preventvibration from transmitting to the photoconductor 24 and the opticalwriting unit 27 via the first plate 112 and the second plate 113.

Here, comparative configurations of a drive device are illustrated inFIGS. 4 and 5. FIG. 4 is a graph of relation of sound pressure level andfrequency of sound emitted when a comparative drive device is driven andFIG. 5 is a schematic cross sectional view illustrating anothercomparative drive device in which an internal gear is used as an idlergear.

The comparative configuration of FIG. 4 includes two gears that arecoaxially disposed and rotate together, for example, in which theinternal gear 116 a and the external gear 116 b are disposed together.With this configuration, noise having two peaks, sound 1 and sound 2,are heard as indicated in the graph of FIG. 4. The sound 1 is a noisehaving a gear mesh frequency of the meshing portion of the internal gear116 a and the motor gear 111 a. The sound 2 is a noise having a gearmesh frequency of the meshing portion of the external gear 116 b and theoutput gear 118.

In this case, respective countermeasures to vibration and noise of thegear mesh frequencies are taken. For example, in a case in whichHelmholtz sound absorbers are used to restrain the noise, one Helmholtzsound absorber for reducing the gear mesh frequency of the sound 1 ofFIG. 4 and another Helmholtz sound absorber for reducing the gear meshfrequency of the sound 2 of FIG. 4 are disposed around the comparativedrive device. However, this configuration is likely to increase the sizeof an image forming apparatus. Further, in order to prevent the defectimage generated due to vibration occurred in the meshing portion, theoptical components and units of the optical writing unit 27 are designednot to resonate with the whole gear mesh frequencies. Accordingly, thecountermeasures to vibration cannot be taken easily. Similarly, it isdifficult to prevent plates and motors from resonating with the wholegear mesh frequencies.

In order to address the inconvenience, the output gear 118 can be meshedwith the internal gear 116 a, so that the internal gear 116 a is used asan idler gear in another comparative configuration of the drive deviceillustrated in FIG. 5. According to the comparative drive deviceillustrated in FIG. 5, the gear mesh frequency of the meshing portion ofthe internal gear 116 a and the motor gear 111 a can be the same as thegear mesh frequency of the meshing portion of the internal gear 116 aand the output gear 118. However, in this comparative configuration, areduction ratio is determined based on the number of teeth of the motorgear 111 a and the number of teeth of the output gear 118. Therefore, inorder to obtain a high reduction ratio, the diameter of the output gear118 increases in size, and the size of the image forming apparatus 100also increases.

By contrast, in the configuration illustrated in FIG. 3, the finalreduction ratio is determined based on a value obtained by multiplyingthe reduction ratio of the internal gear 116 a and the motor gear 111 aby a reduction ratio of the output gear 118 and the external gear 116 b.As a result, a large reduction ratio can be obtained even if thediameter of each gear is small, and therefore an increase in size of theimage forming apparatus 100 can be prevented.

Further, in the comparative configuration illustrated in FIG. 5, themotor gear 111 a and the output gear 118 are meshed with the internalgear 116 a. Therefore, abrasion of the teeth of the internal gear 116 aadvances quickly, resulting in the early end of service life of theinternal gear 116 a.

In order to address the inconvenience, the drive device 110 according tothe present embodiment adjusts respective modules of the motor gear 111a, the internal gear 116 a, the external gear 116 b, and the output gear118 such that a difference of the gear mesh frequency of the meshingportion of the internal gear 116 a and the motor gear 111 a and the gearmesh frequency of the meshing portion of the external gear 116 b and theoutput gear 118 is set to 100 Hz or smaller.

Table 1 below indicates the number of teeth, modules, the number ofrotations, the gear mesh frequencies of respective gears.

TABLE 1 No. Gear No. or mesh Reference of Rotations frequency NumberTeeth Module (rpm) (Hz) Motor With 111a 17 0.4 1350 383 External TeethReduction With 116a 79 0.4 291 383 Gear Internal Teeth With 116b 59 0.5286 External Teeth Output With  118 33 0.5 519 286 Gear External Teeth

In the present embodiment, by adjusting the number of teeth, modules,and the number of rotations of respective gears, the difference of thegear mesh frequency of the meshing portion of the motor gear 111 a andthe internal gear 116 a and the gear mesh frequency of the meshingportion of the external gear 116 b and the output gear 118 is set to 100Hz or smaller.

FIG. 6A is a graph illustrating the effect of sound absorption by usingthe Helmholtz sound absorber. FIG. 6B is a graph illustrating anothereffect of sound absorption by using the Helmholtz sound absorber.

The Helmholtz sound absorber used in FIGS. 6A and 6B absorbs thefrequency of 1000 Hz. As illustrated in FIGS. 6A and 6B, the Helmholtzsound absorber absorbed sound in a range of 1000 Hz±50 Hz. Accordingly,the Helmholtz sound absorber can absorb sound in a range of 100 Hz.Therefore, by setting the difference of the gear mesh frequencies of themeshing portions of gears to 100 Hz or smaller, a noise heard from eachmeshing portion can be absorbed by a single Helmholtz sound absorber.For example, in the present embodiment, a noise heard from each meshingportion can be absorbed by a Helmholtz sound absorber having a resonancefrequency in a resonance space in a range from 286 Hz to 383 Hz.

Further, the gear mesh frequencies of the meshing portions of gears canbe set to values close to each other. Therefore, the optical componentsand units of the optical writing unit 27, the plates, and the motor canbe easily designed to be free from resonance with the whole gear meshfrequencies.

In the present embodiment, the motor is rotated at high speed todecelerate significantly by meshing the internal gear and the motorgear. Therefore, the meshing portion of the motor gear and the internalgear is most likely to vibrate and generate noise. Therefore, in thepresent embodiment, the module of the internal gear 116 a and the moduleof the motor gear 111 a are set to be smaller than the module of therest of gears. By reducing the module of gear, the size of gear toothcan be reduced and the contact ratio of the motor gear 11 a and theinternal gear 116 a can be increased. By so doing, vibration and noisein the meshing portion of the motor gear and the internal gear can bereduced.

Further, as indicated in Table 1, at least one of a pair of gears thatform a meshing portion has a prime number of teeth.

As in Table 1, in the present embodiment, the motor gear 111 a, theinternal gear 116 a, and the external gear 116 b have respective primenumbers of teeth. Consequently, any tooth on the at least one of thepair of gears contacts each tooth on the other of the pair of gearsbefore encountering the same tooth. Since the shape of each tooth on agear is different from another tooth on the same gear due tomanufacturing error, tooth contacts of gears in mesh vary depending oncombinations of teeth of gears. In a case in which a tooth on a gearcontacts the same tooth on the other gear with each cycle, the teethcontact in the same manner, which accelerates local wear of the teeth ofthe gears. However, a gear whose tooth counts is prime can contact adifferent tooth of the other gear each time the pair of gears mesh witheach other. This configuration can spread the wear evenly over the wholeteeth of the pair of gears, resulting in an increase in the service lifeof the gears.

Next, a description is given of a drive device 110A according to avariation of the present embodiment of this disclosure.

Variation 1.

FIG. 7 is a schematic cross sectional view illustrating the drive device110A of Variation 1. As illustrated in FIG. 7, the drive device 110Aincludes the motor gear 111 a, the internal gear 116 a, the externalgear 116 b, and the output gear 118, which are helical gears. With thisconfiguration, the contact ratio of the gears can be increased, andtherefore the meshing vibration and noise can be further restrained.

Further, in Variation 1, it is preferable that a direction of torsion ofteeth of the internal gear 116 a is set such that a thrust force that isgenerated when the internal gear 116 a rotates directs to the motorside, as indicated by arrow F1 in FIG. 7. Specifically, when the motorshaft is viewed in the axial direction from a side close to thedeveloping roller (hereinafter, the developing roller side), if themotor shaft rotates in the counterclockwise direction, the gear teethare twisted in a right direction. By contrast, if the motor shaftrotates in the clockwise direction, the gear teeth are twisted in a leftdirection. That is, the gear teeth are twisted such that the twistedteeth of the helical gear on the developing roller side is disposed to adownstream side from the twisted teeth of the helical gear on the motorside in a direction of rotation of the helical gear. By so doing, whenthe motor gear 111 a is rotated, a thrust force to the developing rollerside is generated to press the driving motor 111 against the first plate112. With this configuration, the posture of the driving motor 111 canbe maintained, and therefore occurrence of the meshing vibration can berestrained reliably.

Further, a direction of torsion of teeth of the external gear 116 b isset such that a thrust force directs to the developing roller side, asindicated by arrow F2 in FIG. 7, which is an opposite direction of thethrust force of the internal gear 116 a. Specifically, the gear teeth ofthe external gear 116 b are twisted in the same direction as the motorgear 111 a, which is a reverse direction of the twisted teeth of theinternal gear 116 a. Consequently, the thrust force of the internal gear116 a is eliminated by the thrust force of the external gear 116 b, andtherefore the reduction gear 116 moves to the motor side. Therefore, thereduction gear 116 is prevented from rotating while contacting the firstplate 112. Accordingly, the good rotation of the reduction gear 116prevents rotation speed errors, and therefore the developing roller canbe rotated reliably.

Further, the external gear 116 b of the reduction gear 116 is disposedon an outer circumference of the internal gear 116 a whose teeth areformed on an inner circumference of the cylindrical portion. Bydisposing the external gear 116 b on the outer circumference of theinternal gear 116 a, when compared with the reduction gear 116 of thedrive device 110 illustrated in FIG. 3, the reduction gear 116 of thedrive device 110A illustrated in FIG. 7 can reduce the length in theaxial direction. Accordingly, the size of the drive device 110A can bereduced.

Table 2 below indicates the number of teeth, modules, the number ofrotations, the variation meshing frequencies of respective gears in thedrive device 110A of Variation 1.

TABLE 2 No. Gear No. or mesh Reference of Rotations frequency NumberTeeth Module (rpm) (Hz) Motor With 111a 12 0.5 1800 360 External TeethReduction With 116a 79 0.5 273 360 Gear Internal Teeth With 116b 79 0.6360 External Teeth Output With  118 33 0.6 655 360 Gear External Teeth

Similar to the drive device 110, in the drive device 110A of Variation1, the external gear 116 b is coaxially disposed with the internal gear116 a to rotate together. However, as indicated in Table 2, by adjustingthe module of each gear, the number of teeth of the internal gear 116 ais set the same as the number of teeth of the external gear 116 b. By sodoing, the gear mesh frequency of the meshing portion of the motor gear111 a and the internal gear 116 a is set the same as the gear meshfrequency of the meshing portion of the external gear 116 b and theoutput gear 118.

Further, a torsional angle of the twisted teeth of each gear isdetermined based on the module of a pair of gears forming the meshingportion and a distance between the shafts of these gears. Due to thelayout of an image forming apparatus, respective locations of a motorsand a developing roller are limited. Therefore, even if the module ofeach gear is set appropriately and the difference of the gear meshfrequencies of the meshing portions is set to 100 Hz or smaller, acenter distance between the gears cannot be set preferably. Accordingly,the teeth of one gear cannot mesh with the teeth of the other gearreliably. In that case, by adjusting the torsional angle of the twistedteeth of the helical gear, a pitch distance of gears can be adjusted,and therefore the teeth can be meshed with each other reliably. That is,the torsional angle of the twisted teeth of each gear is determinedbased on the module of a pair of gears forming the meshing portion andthe center distance of the pair of gears.

Variation 2.

FIG. 8 is a schematic cross sectional view illustrating a drive device110B of Variation 2.

The drive device 110B of Variation 2 includes a reduction gear 126including a first internal gear 126 a and a second internal gear 126 b.The first internal gear 126 a is meshed with the motor gear 111 a andthe second internal gear 126 b is meshed with the output gear 118.

In Variation 2, the output gear 118 meshes with an internal gear. Withthis configuration, the contact ratio of the output gear 118 and thesecond internal gear 126 b increases, and therefore vibration and noiseproduced by gear operation can be restrained. Further, the secondinternal gear 126 b can cover the meshing portion of the second internalgear 126 b and the output gear 118, and therefore the meshing noise canbe blocked by the second internal gear 126 b. The second internal gear126 b is shaped like a cylinder and the motor side is open. Therefore,meshing noise is heard from the second internal gear 126 b. However, thesecond plate 113 is disposed facing the opening of the second internalgear 126 b. Therefore, the meshing noise can be prevented from beingheard outside the drive device 110A from the second plate 113.

By so doing, vibration and noise in the meshing portion of the outputgear 118 and an internal gear can be reduced when compared with themeshing portion of the output gear 118 and an external gear.

Table 3 below indicates the number of teeth, modules, the number ofrotations, the variation meshing frequencies of respective gears in thedrive device 110B of Variation 2.

TABLE 3 No. Gear No. or mesh Reference of Rotations frequency NumberTeeth Module (rpm) (Hz) Motor With 111a 15 0.3 1200 300 External TeethReduction With 126a 80 0.3 225 300 Gear First Internal Teeth With 126b78 0.6 293 Second Internal Teeth Output With  118 21 0.6 836 293 GearExternal Teeth

Similar to the drive device 110 and the drive device 110A, in the drivedevice 110B of Variation 2, the first internal gear 126 a and the secondinternal gear 126 b are coaxially disposed. However, as indicated inTable 3, by adjusting the modules of respective gears, the difference ofthe gear mesh frequency of the meshing portion of the motor gear 111 aand the first internal gear 126 a and the gear mesh frequency of themeshing portion of the second internal gear 126 b and the output gear118 is set to 100 Hz or smaller.

Variation 3.

FIG. 9 is a schematic cross sectional view illustrating a drive device110C of Variation 3.

The drive device 110C of Variation 3 includes a reduction gear 136including an internal gear 136 a and a pulley 136 b. Further, an outputpulley 138 is mounted on the development driving shaft 81 a. Inaddition, a timing belt 137 is wound around the pulley 136 b and theoutput pulley 138 so as to contact teeth of the pulley 136 b and teethof the output pulley 138.

In Variation 3, the drive device 110C transmits a drive force from thereduction gear 136 to the development driving shaft 81 a via the timingbelt 137. Therefore, even if the driving motor 111 is separated awayfrom the developing roller 81, the drive power transmission can beperformed with a small number of components.

Table 4 below indicates the number of teeth, modules, pulley toothshapes, the number of rotations, the variation meshing frequencies ofrespective gears in the drive device 110C of Variation 3.

TABLE 4 Module/ No. Gear No. Pulley or Mesh Reference of Tooth RotationsFrequency Number Teeth Shape (rpm) (Hz) Motor With 111a 9 0.5 1500 225External Teeth Reduction With 136a 45 0.5 300 225 Gear Internal TeethWith 136b 40 S1.5M 200 Pulley Output With  138 37 S1.5M 324 200 GearPulley

The configuration of the drive device 110C of Variation 3 has threemeshing portions, which are a meshing portion of the motor gear 111 aand the internal gear 136 a, a meshing portion of the pulley 136 b andthe timing belt 137, and a meshing portion of the timing belt 137 andthe output pulley 138. However, the timing belt 137 acts as an idlergear. Accordingly, the gear mesh frequency of the meshing portion of thepulley 136 b and the timing belt 137 is the same as the gear meshfrequency of the meshing portion of the timing belt 137 and the outputpulley 138. Therefore, in the configuration of the drive device 110C ofVariation 3, it is likely that the gear mesh frequency of the meshingportion of the timing belt and the pulley that is coaxially disposedwith the internal gear is different from the gear mesh frequency of themeshing portion of the internal gear and the motor gear.

However, as indicated in Table 4, by adjusting the modules of respectivegears and the pulley tooth shapes of respective pulleys, the differenceof the gear mesh frequency of the motor gear 111 a and the internal gear136 a and the gear mesh frequency of the meshing portion of the pulleysand the timing belt is set to 100 Hz or smaller.

Variation 4.

FIG. 10 is a schematic cross sectional view illustrating a drive device110D of Variation 4. Table 5 below indicates the number of teeth,modules, the number of rotations, the variation meshing frequencies ofrespective gears in the drive device 110D of Variation 4.

TABLE 5 Gear Mesh No. or Frequency (Hz) Reference No. of RotationsPrimary Secondary Number Teeth Module (rpm) Element Element Motor With111a 15 0.3 2300 575 1150 External Teeth Reduction With 116a 84 0.3 411575 1150 Gear Internal Teeth With 116b 160 0.3 1095 2190 External TeethOutput With  118 51 0.3 1289 1095 2190 Gear External Teeth

In Variation 4, as indicated in Table 5, the primary component of thegear mesh frequency of the meshing portion of the external gear 116 band the output gear 118 is different from the secondary component of thegear mesh frequency of the meshing portion of the motor gear 111 a andthe internal gear 116 a by 100 Hz or smaller.

Depending on the configuration of a drive device, there is a case wherethe noise level of the secondary component of the gear mesh frequency ofthe meshing portion of the motor gear 111 a and the internal gear 116 ais greater than the primary component of the gear mesh frequency of themeshing portion of the external gear 116 b and the output gear 118.

It is to be noted that the primary component of a gear mesh frequency isa gear mesh frequency that is calculated based on the number ofrotations of gears and the number of teeth of the gears. The primarycomponent of the gear mesh frequency is expressed by (Z*n/60), where “n”represents the number of rotations of a gear and “Z” represents thenumber of teeth of the gear. By contrast, the secondary component of agear mesh frequency is either one of a frequency of 2 or more integralmultiples of the primary component and a frequency of ½ or more integraldivisions of the primary component. Generally, a noise of the meshingportion corresponds to a noise of the meshing portion of the primarycomponent. However, when the first plate 112 and the second plate 113resonate with the secondary component of the gear mesh frequency, forexample, the noise of the secondary component may increase to exceed thenoise of the meshing portion of the primary component.

It is preferable that a drive device rotates a motor at high speed anddecelerates the speed significantly at the drive transmitter to obtain ahigh torque. Therefore, the drive device preferably has the smallernumber of teeth of the motor gear and the greater number of teeth of aninternal gear. Consequently, a module of the motor gear and the internalgear is previously determined, and the gear mesh frequency of themeshing portion of the motor gear and the internal gear may bedetermined accordingly. As a result, even if the secondary component ofthe gear mesh frequency of the meshing portion of the motor gear and theinternal gear resonates with the plate, the module of the motor gear andthe internal gear cannot be changed easily to prevent resonance of thesecondary component and the plate. Accordingly, in this case,countermeasures are taken to prevent noise and vibration with respect tothe secondary component of the meshing portion of the motor gear and theinternal gear.

In Variation 4, the module of the external gear and the output gear isset such that the gear mesh frequency of the meshing portion of theexternal gear and the output gear corresponds to the secondary componentof the gear mesh frequency of the meshing portion of the motor gear andthe internal gear. Accordingly, by taking the countermeasures to preventnoise and the vibration with respect to the secondary component of thegear mesh frequency of the motor gear and the internal gear, the noiseand vibration with respect to the gear mesh frequency of the externalgear and the output gear can be reduced and restrained.

Next, a description is given of detailed examples of countermeasures tonoise reduction of a drive device.

FIG. 11 is a schematic cross sectional view illustrating an example ofnoise reduction measures.

A sound absorbing device 140 illustrated in FIG. 11 is included to adrive device in order to absorb sound generated due to vibration of thegear mesh frequency and reduce the sound of the drive device. It is tobe noted that the drive device illustrated in FIG. 11 corresponds to thedrive device 110A. As illustrated in FIG. 11, the sound absorbing device140 includes a sound absorbing plate 141 and multiple Helmholtz soundabsorbers 142. The sound absorbing plate 141 that is disposed facing amotor side face of the first plate 112 has multiple openings. Themultiple Helmholtz sound absorbers 142 are disposed at the multipleopenings of the sound absorbing plate 141.

Each of the Helmholtz sound absorbers 142 functions as a resonator thatincludes a resonance space 142 b having a volume (V) and a resonancepath 142 a having a length (L) and a cross sectional area (S) to causethe resonance space 142 b to communicate with outside space. Theresonance frequency f of each of the Helmholtz sound absorbers 142 isexpressed by an equation, “f=(c/2π)·(S/V−(L+6))½”. Where “V” representsthe volume of the resonance space 142 b, “L” represents a length of theresonance path 142 a, “S” represents a cross sectional area of theresonance path 142 a, “c” represents a sound speed, and “8” representsan open end correction value. The open end correction value δ is a valueto correct the effect of resonance near an entrance of the resonancepath 142 a. The value around 0.5 is generally employed.

The resonance frequency f of each of the Helmholtz sound absorbers 142is set in a range from the lowest frequency to the highest frequency ofthe gear mesh frequencies of the meshing portions of respective gears.Specifically, the gear mesh frequency of each meshing portioncorresponds to the values of Table 1, the resonance frequency of each ofthe Helmholtz sound absorbers 142 is set in a range from 286 Hz to 383Hz. Further, when the drive device 110A of Variation 1 is employed, theresonance frequency f of the Helmholtz sound absorbers 142 is set to bearound 360 Hz. When the drive device 110B of Variation 2 is employed,the resonance frequency f of the Helmholtz sound absorbers 142 is set tobe around 300 Hz. When the drive device 110C of Variation 3 is employed,the resonance frequency f of the Helmholtz sound absorbers 142 is set tobe around 200 Hz. When the drive device 110D of Variation 4 is employed,the resonance frequency f of the Helmholtz sound absorbers 142 is set tobe around 1100 Hz.

As previously described with reference to FIGS. 6A and 6B, the Helmholtzsound absorbers 142 can absorb sound of ±50 Hz relative to apredetermined sound absorbing frequency.

In a case in which the difference of the gear mesh frequency of themeshing portion of the internal gear 116 a and the motor gear 111 a andthe gear mesh frequency of the meshing portion of the external gear 116b and the output gear 118 exceeds 100 Hz, the sound absorbing device 140has the following configuration so that the gear mesh frequency of themeshing portion of the internal gear 116 a and the motor gear 111 a andthe gear mesh frequency of the meshing portion of the external gear 116b and the output gear 118 are reduced and restrained reliably.Specifically, the Helmholtz sound absorbers to absorb noise having thegear mesh frequency of the meshing portion of the external gear 116 band the output gear 118 are disposed so as to overlap the Helmholtzsound absorbers to absorb noise having the gear mesh frequency of themeshing portion of the internal gear 116 a and the motor gear 111 a. Inthis case, the drive device and the image forming apparatus includingthe drive device increase in size.

As an alternative configuration of the drive device, one half of themultiple Helmholtz sound absorbers is assigned to absorb noise havingthe gear mesh frequency of the meshing portion of the internal gear 116a and the motor gear 111 a and the other half is assigned to absorbnoise having the gear mesh frequency of the meshing portion of theexternal gear 116 b and the output gear 118. However, in this case, theHelmholtz sound absorbers cannot absorb noise when the resonancefrequency corresponds to the gear mesh frequency of the meshing portionof the external gear and the output gear inserted in the Helmholtz soundabsorber of the gear mesh frequency of the meshing portion of theinternal gear and the motor gear.

However, in the present embodiment, as indicated in Tables 1 through 5,the difference of the gear mesh frequencies of respective gears is setto 100 Hz or smaller. Therefore, by setting the resonance frequency f ofthe Helmholtz sound absorbers 142 as described above, a single Helmholtzsound absorber can absorb noise having the gear mesh frequencies of thewhole meshing portions of respective gears.

FIG. 12 is a schematic cross sectional view illustrating another exampleof noise reduction measures.

As illustrated in FIG. 12, the driving motor 111 and a drive powertransmission mechanism 150 are surrounded by Helmholtz sound absorbers241 and 244, respectively. The drive power transmission mechanism 150 isdisposed between the first plate 112 and the second plate 113 andincludes multiple gears. Specifically, a motor sound absorbing member242 includes a cylindrical resin molding product and is attached to thefirst plate 112 surrounding the driving motor 111. In addition, a drivetransmission sound absorbing member 243 includes a cylindrical resinmolding product and is attached to the first plate 112 and the secondplate 113 surrounding the drive power transmission mechanism 150.

FIG. 13 is a perspective view illustrating the motor sound absorbingmember 242.

As illustrated in FIG. 13, the motor sound absorbing member 242 is acylindrical resin molding product. The motor sound absorbing member 242includes multiple cavity sections 241 a and attaching portions 241 c.The multiple cavity sections 241 a are disposed along a circumferentialdirection of the motor sound absorbing member 242. Each of the multiplecavity sections 241 a has an opening on one side. Each of the multiplecavity sections 241 a has a cut 241 b in an inner circumferentialsurface on the opening side. The attaching portions 241 c are disposedon an outer circumference of the motor sound absorbing member 242 tosecure the motor sound absorbing member 242 to the first plate 112 withscrew.

As illustrated in FIG. 12, the motor sound absorbing member 242 isattached to the first plate 112. By so doing, respective resonancespaces of the Helmholtz sound absorber 241 are defined by the cavitysections 241 a and the first plate 112. Further, respective resonancepaths of the Helmholtz sound absorber 241 are defined by the first plate112 and the cuts 241 b. Accordingly, the multiple Helmholtz soundabsorbers 241 are disposed surrounding the driving motor 111.

The resonance frequency f of the multiple Helmholtz sound absorbers 241defined by the motor sound absorbing member 242 and the first plate 112is set to a value between the lowest frequency and the highest frequencyof the gear mesh frequencies of the multiple meshing portions. By sodoing, the driving motor 111 vibrates due to vibration occurred in themeshing portion, so that the vibration of the gear mesh frequency can beabsorbed by the multiple Helmholtz sound absorbers 241 disposed aroundthe driving motor 111.

The drive transmission absorbing member 243 includes cavity sections 244a aligned in the axial direction. Each of the cavity sections 244 aincludes a cut 244 b. The two cavity sections 244 a disposed on themotor side have respective openings that are blocked by the first plate112. By so doing, respective resonance spaces of the Helmholtz soundabsorbers 244 are formed. Further, respective resonance paths of theHelmholtz sound absorbers 244 are defined by the first plate 112 and thecuts 244 b. Further, the cavity sections 244 a disposed on thedeveloping roller side have respective openings that are blocked by thesecond plate 113. By so doing, respective resonance spaces of theHelmholtz sound absorbers 244 are formed. Further, respective resonancepaths of the Helmholtz sound absorbers 244 are defined by the cuts 244 band the second plate 113. Accordingly, the multiple Helmholtz soundabsorbers 244 are disposed surrounding the drive power transmissionmechanism 150.

The resonance frequency f of the multiple Helmholtz sound absorbers 244defined by the drive transmission absorbing member 243, the first plate112, and the second plate 113 is set to a value between the lowestfrequency and the highest frequency of the gear mesh frequencies of themultiple meshing portions. Therefore, the multiple Helmholtz soundabsorbers 244 can absorb noise having the gear mesh frequencies of thewhole meshing portions of respective gears.

A Helmholtz sound absorber that absorbs sound incident to the absorber,and therefore is effective to dispose around the sound source. In a casein which the Helmholtz sound absorbers are disposed around the soundsource such as the drive power transmission mechanism 150 and thedriving motor 111, at least four sound absorbing device 140 are disposedon each side of the sound source. This configuration increases thenumber of components, resulting in an increase in costs.

However, the sound source can be surrounded by the Helmholtz soundabsorbers on each side when the motor sound absorbing member 242 of FIG.13 is attached to the plate of the drive device 110 having theconfiguration illustrated in FIG. 12. Consequently, the number ofcomponents of the drive device can be reduced when compared with theconfiguration employing the sound absorbing device 140. Accordingly,this configuration can reduce the cost of the drive device.

FIG. 14 is a schematic cross sectional view illustrating yet anotherexample of noise reduction measures.

In FIG. 14, a structure around the driving motor 111 and the drive powertransmission mechanism 150 is made in labyrinth structure to reduce thenoise from the driving motor 111 and the drive power transmissionmechanism 150.

As illustrated in FIG. 14, the drive device such as the drive device110A includes a cover 151 to cover the driving motor 111. An end portion151 b of the cover 151 is bent toward the first plate 112. The leadingedge of the end portion 151 b faces the first plate 112 with apredetermined gap. The cover 151 includes a first motor side rib 151 athat extends toward the first plate 112. A second motor side rib 112 bis disposed between the first motor side rib 151 a and the end portion151 b of the cover 151 and extending from the first plate 112 toward thecover 151. The second motor side rib 112 b is disposed such that atleast a portion of the leading edge faces the end portion 151 b of thecover 151 and the first motor side rib 151 a. According to the layout ofthe drive device with the drive power transmission mechanism 150illustrated in FIG. 14, an air flow path is made as a labyrinth air flowpath having multiple turns and corners to communicate from the inside ofthe cover 151 to the outside of the cover 151.

Noise generated when the driving motor vibrates due to vibrationoccurred in each meshing portion is blocked by the cover. In addition,noise spreading in the vertical direction in FIG. 14 is diffracted bythe first motor side rib 151 a and the second motor side rib 112 b, andis then leaked. Each time sound is diffracted, the sound attenuates.Therefore, when the sound is leaked from a gap between the end portion151 b of the cover 151 and the first plate 112, the sound is attenuatedsufficiently. Consequently, the leaked sound does not turn into noiseharsh to a user or uses. In addition, heat of the driving motor can beescaped to the outside by passing through the labyrinth air flow path.Therefore, an increase in temperature around the drive device can beprevented.

A first power transmission mechanism side rib 112 a is disposedextending to the developing roller side from the first plate 112 on aside facing the second plate 113. A second power transmission mechanismside rib 113 a is disposed extending to the motor side from the secondplate 113 on a side facing the first plate 112. The second powertransmission mechanism side rib 113 a is disposed outside from the firstpower transmission mechanism side rib 112 a. At least a portion of theleading edge of the second power transmission mechanism side rib 113 ais disposed facing the first power transmission mechanism side rib 112a. Accordingly, an air flow path is made as a labyrinth air flow pathhaving one turn to communicate from the inside of the drive powertransmission mechanism 150 to the outside of the cover 151. With thisstructure, sound is diffracted by the first power transmission mechanismside rib 112 a and the second power transmission mechanism side rib 113a before leaking from the drive device. Therefore the leading sound canbe attenuated sufficiently.

In the labyrinth structure, high frequency sound can be attenuatedreliably. It is because low frequency sound has lower attenuation effectdue to diffraction than high frequency sound. In a case in which onegear of coaxially mounted gears is a high gear mesh frequency and theother gear is a low meshing frequency, if noise reduction measures aretaken using the labyrinth structure, noise having the gear meshfrequency of the meshing portion of the other gear cannot be reduced.However, in the present embodiment, the modules of the gears areadjusted based on the high gear mesh frequency of the meshing portion ofthe one gear to set the difference of the gear mesh frequencies of themeshing portions to 100 Hz or smaller. By so doing, the gear meshfrequencies of the whole meshing portions can be made the high gear meshfrequency. Furthermore, when providing the labyrinth structure, the gearmesh frequencies of the whole meshing portions can be reduced reliably.

The noise reduction measures with the labyrinth structure is effectiveto sound having high frequency. Therefore, as described in Variation 4,the noise reduction measures are effective when the modules of therespective gears are adjusted such that the noise level of the secondarycomponent of integral multiples of the gear mesh frequency of themeshing portion of the motor gear 111 a and the internal gear 116 a isthe highest and that the gear mesh frequencies of the other meshingportions correspond to the gear mesh frequency of the secondarycomponent.

In the above-described embodiments, the developing roller functions as adrive transmission object that is driven by the drive device. However,the configuration is not limited thereto. For example, thephotoconductor can function as the drive transmission object.

The configurations according to the above-descried embodiments are notlimited thereto. This disclosure can achieve the following aspectseffectively.

Aspect 1.

A drive device (for example, the drive device 110) includes a drivemotor (for example, the driving motor 111) and a plurality of gears (forexample, the motor gear 111 a, the internal gear 116 a, the externalgear 116 b, and the output gear 118). The plurality of gears are drivenby the drive motor and includes at least two gears disposed coaxiallywith each other. The plurality of gears have a plurality of meshingportions. Each meshing portion is formed between a pair of gears out ofthe plurality of gears. A difference between respective gear meshfrequencies of the plurality of meshing portions is set to be equal toor smaller than 100 Hz.

As described in the embodiments above, the comparative drive device wasexamined to find causes to generate noises having different frequenciesfrom each other. It was found through the examination that the gear meshfrequencies of respective meshing portions of the coaxially disposedgears are different from each other, which was a cause of occurrence ofnoises having the different frequencies. Accordingly, the gear meshfrequency is determined based on the number of teeth of a gear and thenumber of rotations of the gear. Therefore, when a gear mesh frequencyis calculated based on the number of teeth of one gear out of a pair ofgears and the number of rotations of the one gear or based on the numberof teeth of the other gear out of the pair of gears and the number ofrotations of the other gear, the same calculation result is obtained.Therefore, in a case in which the whole gears are not disposedcoaxially, in other words, in which the whole gears that are disposedbetween the motor gear of the motor and the output gear that outputs adriving force to a drive transmission object such as the developingroller are idler gears, the whole gear mesh frequencies of the meshingportions of the gears are identical to each other. However, two or moregears disposed coaxially are different in gear mesh frequency when thetwo or more gears have the different numbers of teeth from each other.Therefore, in a configuration in which two or more gears are disposedcoaxially, some gear mesh frequencies of the meshing portions of the twoor more gears may be different from each other.

In order to address the inconvenience, in Aspect 1, the differencebetween respective gear mesh frequencies of the meshing portions is setto be equal to or smaller than 100 Hz, so that a difference betweenvibrations generated in the meshing portions of the gears and adifference between the frequencies of noises occurred due to thevibrations are set to be equal to or smaller than 100 Hz.

A sound absorbing device that is used to reduce the noise can absorbsound in a range of 100 Hz. For example, the Helmholtz sound absorberthat functions as the sound absorbing device can absorb sound in a rangeof 100 Hz (±50 Hz relative to a target resonance frequency), asillustrated in FIG. 6. Therefore, noise generated due to vibration inthe meshing portions of the gears can be absorbed by providing theHelmholtz sound absorber with a target frequency set between a lowestfrequency and a highest frequency out of the whole gear mesh frequenciesof the meshing portions of the gears.

As described above, if a predetermined single measure is taken, noisegenerated due to vibration at the gear mesh frequencies of the wholemeshing portions of the gears can be reduced. Therefore, the noisereduction measure can be taken easily when compared with a predeterminednoise reduction measure taken for each gear mesh frequency of themeshing portions. Consequently, noise can be reduced easily.

Aspect 2.

In Aspect 1, the plurality of meshing portions include a referencemeshing portion having a reference gear mesh frequency. A greatest soundcomponent is greatest in sound level out of sound components havingintegral multiples of the reference gear mesh frequency of the referencemeshing portion and sound components having integral divisions of thereference gear mesh frequency of the reference meshing portion, and adifference between a gear mesh frequency of the greatest sound componentand each gear mesh frequency of sound components of the rest of theplurality of meshing portions is set equal to or smaller than 100 Hz.

According to this configuration, as described in Variation 4, thegreatest sound component is greatest in sound level out of soundcomponents (for example, the primary component and the secondarycomponent) of the reference gear mesh frequency of the reference meshingportion, and a difference between the gear mesh frequency of thegreatest sound component and each gear mesh frequency of the othermeshing portions is set to be equal to or smaller than 100 Hz. By sodoing, noise of the drive device and the image forming apparatus can bereduced and restrained.

Aspect 3.

In Aspect 2, the plurality of gears include a motor gear (for example,the motor gear 111 a) of the drive motor and a mating gear (for example,the internal gear 116 a) meshing with the motor gear. The motor gear andthe mating gear mesh with each other in the reference meshing portion.

According to this configuration, as described in Variation 4, themeshing portion of the motor gear and the mating gear is the referencemeshing portion. By so doing, the motor gear and the mating gear can beconstructed not to meet the gear mesh frequency thereof with the gearmesh frequencies of the other meshing portions but to obtain a highertorque. Specifically, in this configuration, the number of teeth of themotor gear is reduced as possible and the number of teeth of the matinggear is increased as possible. Then, by meeting the gear meshfrequencies of the other meshing portions of the other gears with thereference gear mesh frequency of the reference meshing portion, thedrive device can provide a higher torque and perform noise reductionmeasures easily.

Aspect 4.

In any one of Aspect 1 through Aspect 3, a module of each gear of theplurality of gears is set such that a difference between the gear meshfrequencies of the meshing portions are equal to or smaller than 100 Hz.

According to this configuration, by adjusting the module of each gear, adifference between the gear mesh frequencies of the meshing portions canbe set to be equal to or smaller than 100 Hz.

Aspect 5.

In any one of Aspect 1 through Aspect 4, the plurality of gears includea helical gear.

According to this configuration, as described in the as described in theembodiments above, the contact ratio can be increased, and thereforevibration and noise in the meshing portions can be prevented.

Aspect 6.

In Aspect 5, the helical gear has a torsion angle based on a module ofthe pair of gears that form the meshing portion and a distance betweenrespective axes of the pair of gears.

According to this configuration, as described in Variation 1, thediameter of a pitch circle of a gear can be adjusted based on thetorsion angle. Therefore, according to this configuration, the torsionangle of the helical gear is set based on the module of the pair ofgears that includes a meshing portion and a distance between therespective axes of the pair of gears. Therefore, the teeth can be meshedreliably.

Aspect 7.

In any one of Aspect 1 through Aspect 6, the number of teeth of at leastone gear of the pair of gears is a prime number.

According to this configuration, as described in the embodiments above,meshing of the same teeth each time the pair of gears contact can beprevented, and therefore each tooth wears evenly. Consequently, theservice life of the gears can increase.

Aspect 8.

In any one of Aspect 1 through Aspect 7, the plurality of gears includea motor gear of the drive motor and a mating gear meshing with the motorgear, and a module of the motor gear and a module of the mating gear aresmaller than modules of the rest of the plurality of gears.

As described in the embodiments above, after the driving motor isrotated at high speed, the speed is decelerated significantly by meshingthe motor gear and the mating gear. Therefore, the meshing portion ofthe motor gear and the mating gear is most likely to vibrate andgenerate noise.

Therefore, the module of the mating gear and the module of the motorgear are set to be smaller than the module of the rest of the pluralityof gears. By so doing, the size of gear tooth can be reduced, and thecontact ratio of the motor gear and the mating gear can be increased.According to this configuration, occurrence of vi and noise in themeshing portion of the motor gear and the mating gear can be reduced,and therefore noise and vibration of the drive device and the imageforming apparatus can be prevented effectively.

Aspect 9.

In any one of Aspect 1 through Aspect 8, the motor gear (for example,the motor gear 111 a) and the mating gear (for example, the internalgear 116 a) includes an internal gear.

As described in the embodiments above, after the driving motor isrotated at high speed, the speed is decelerated significantly by meshingthe motor gear and the mating gear. Therefore, the meshing portion ofthe motor gear and the mating gear is most likely to vibrate andgenerate noise.

Therefore, in Aspect 9, the mating gear that meshes with the motor gearis an internal gear (for example, the internal gear 116 a). By so doing,when compared with a configuration in which the mating gear is anexternal gear, the internal gear can increase the contact ratio with themotor gear, and therefore can prevent occurrence of noise and vibrationin the meshing portion. In addition, the internal gear can cover themeshing portion, and therefore the configuration can prevent noisegenerated in the meshing portion from leaking to the outside of thedrive device or the image forming apparatus. Accordingly, occurrence ofvibration and noise in the meshing portion of the motor gear and themating gear can be reduced, and therefore noise and vibration of thedrive device and the image forming apparatus can be preventedeffectively.

Aspect 10.

In Aspect 9, the drive device (for example, the drive device 110)further includes a reinforcing projection (for example, the reinforcingprojections 116 c) mounted on the internal gear (for example, theinternal gear 116 a).

The internal gear includes internal teeth on an inner circumference of acylindrical body. Therefore, when compared with an external gear havingexternal teeth on an outer circumference of a cylindrical body, therigidity of the internal gear is lower.

In order to address this inconvenience, in Aspect 10, the drive deviceincludes the reinforcing projection to reinforce the internal gear. Byso doing, the rigidity of the internal gear can be increased. Therefore,when a driving force is transmitted from the motor gear (for example,the motor gear 111 a), deformation of the internal gear can be reduced.Consequently, abnormal wear of gear teeth and meshing vibration can beprevented.

Aspect 11.

In Aspect 9 or Aspect 10, the internal gear (for example, the internalgear 116 a) has internal helical teeth arranged such that one side farfrom the drive motor (for example, the driving motor 111) is disposeddownstream from an opposite side near the drive motor in a direction ofrotation of the motor gear (for example, motor gear 111 a).

According to this configuration, as described in the embodiments above,a thrust force that directs to the opposite side to the drive motor isgenerated to the motor gear. Therefore, the drive motor can be pressedagainst a positioning member such as a motor support plate to positionthe drive motor. With this configuration, the posture of the drive motorcan be maintained, and therefore occurrence of the meshing vibration canbe restrained reliably.

Aspect 12.

In any one of Aspect 9 through Aspect 11, the internal gear includes acylindrical portion that includes internal teeth mounted on an innercircumferential surface and a drive transmitter mounted on an outercircumferential surface.

According to this configuration, as described in Variation 1, whencompared with a configuration in which the internal gear and theexternal gear are aligned in the axial direction, the length of thereduction gear (for example, the reduction gear 116) can be reduced, andtherefore the size of the drive device can be reduced.

Aspect 13.

In any one of Aspect 1 through Aspect 12, the two gears (for example,the internal gear 116 a and the external gear 116 b) coaxially disposedare integrally formed in a single body and include respective helicalgears having different twist directions from each other.

According to this configuration, by providing the two gears havingrespective helical teeth, the contact ratio can be increased, asdescribed above, and vibration and noise of the respective meshingportion of the two gears that are integrally formed in a single body canbe prevented.

Further, as described in Variation 1, a thrust force of one helical gearof the two gears integrally formed in a single body can eliminate by athrust force of the other helical gear of the two gears. Therefore, thisconfiguration can prevent that the single body (for example, thereduction gear 116) integrally including the two gears moves to oneplate close to the drive motor or another plate close to the developingroller and contacts either one of these plates while rotating.Accordingly, the good rotation of the single body integrally includingthe two gears can prevent rotation speed errors, and therefore a drivetransmission object (for example, the developing roller 81) can berotated reliably.

Aspect 14.

In any one of Aspect 1 through Aspect 13, the drive device (for example,the drive device 110) further includes a sound absorber (for example,the sound absorber 140) to absorb a sound having a gear mesh frequencyof each of the plurality of meshing portions.

According to this configuration, a difference between the gear meshfrequencies of the meshing portions of the plurality of gears is set tobe equal to or smaller than 100 Hz. Therefore, the sound absorber canabsorb noise in each meshing portion by setting the frequency to absorbthe sound in a range from the lowest frequency to the highest frequencyof the gear mesh frequency of each meshing portion.

Aspect 15.

In Aspect 14, the sound absorber includes a resonator (for example, theHelmholtz sound absorber 142). The resonator includes a resonance spaceto acoustically resonate with a sound at a predetermined resonancefrequency and a resonance path communicating with the resonance space toguide the sound from an outside of the resonance space to an inside ofthe resonance space.

According to this configuration, the sound absorber can be formed byproviding the resonance space having a cavity section and an openingthat communicates with the resonance space. With this simpleconfiguration, the noise of the gear mesh frequency of the meshingportion of each pair of gears can be absorbed.

Further, the sound can be absorbed in a range of 100 Hz. By setting adifference between the gear mesh frequencies of the meshing portions ofeach pair of gears to 100 Hz or smaller, a single resonator can absorbnoise of the gear mesh frequency of the meshing portion of each pair ofgears.

Aspect 16.

The drive motor (for example, the driving motor 111) transmits a drivingforce to a drive transmission object. The drive transmission object is adeveloping roller (for example, the developing roller 81). Consequently,noise can be reduced while driving the developing roller.

Aspect 17.

The drive motor (for example, the driving motor 111) transmits a drivingforce to a drive transmission object. The drive transmission object is aphotoconductor (for example, the photoconductor 24). Consequently, noisecan be reduced while driving the photoconductor.

Aspect 18.

An image forming apparatus (for example, the image forming apparatus100) includes the drive device (for example, the drive device 110)according to any one of Aspect 1 through Aspect 17, and an image formingdevice (for example, the process units 26K, 26C, 26M, and 26Y) toreceive a driving force transmitted from the drive device.

According to this configuration, vibration and noise in the meshingportion of the drive device can be prevented easily, and therefore areduction in noise of the drive device and the image forming apparatuscan be achieved and defect images such as banding can be preventedeasily.

The above-described embodiments are illustrative and do not limit thisdisclosure. Thus, numerous additional modifications and variations arepossible in light of the above teachings. For example, elements at leastone of features of different illustrative and exemplary embodimentsherein may be combined with each other at least one of substituted foreach other within the scope of this disclosure and appended claims.Further, features of components of the embodiments, such as the number,the position, and the shape are not limited the embodiments and thus maybe preferably set. It is therefore to be understood that within thescope of the appended claims, the disclosure of this disclosure may bepracticed otherwise than as specifically described herein.

What is claimed is:
 1. A drive device comprising: a drive motor; and aplurality of gears driven by the drive motor, the plurality of gearsincluding at least two gears disposed coaxially with each other, theplurality of gears having a plurality of meshing portions, each meshingportion formed between a pair of gears out of the plurality of gears, adifference between respective gear mesh frequencies of the plurality ofmeshing portions being set to be equal to or smaller than 100 Hz.
 2. Thedrive device according to claim 1, wherein the plurality of meshingportions include a reference meshing portion having a reference gearmesh frequency, and wherein, a greatest sound component is greatest insound level out of sound components having integral multiples of thereference gear mesh frequency of the reference meshing portion and soundcomponents having integral divisions of the reference gear meshfrequency of the reference meshing portion and a difference between agear mesh frequency of the greatest sound component and each gear meshfrequency of sound components of the rest of the plurality of meshingportions is set equal to or smaller than 100 Hz.
 3. The drive deviceaccording to claim 2, wherein the plurality of gears include a motorgear of the drive motor and a mating gear meshing with the motor gear,and wherein the motor gear and the mating gear mesh with each other inthe reference meshing portion.
 4. The drive device according to claim 1,wherein a module of each gear of the plurality of gears is set such thata difference between the gear mesh frequencies of the meshing portionsare equal to or smaller than 100 Hz.
 5. The drive device according toclaim 1, wherein the plurality of gears include a helical gear.
 6. Thedrive device according to claim 5, wherein the helical gear has atorsional angle based on a module of the pair of gears that form themeshing portion and a distance between respective axes of the pair ofgears.
 7. The drive device according to claim 1, wherein the number ofteeth of at least one gear of the pair of gears is a prime number. 8.The drive device according to claim 1, wherein the plurality of gearsinclude a motor gear of the drive motor and a mating gear meshing withthe motor gear, and wherein a module of the motor gear and a module ofthe mating gear are smaller than modules of the rest of the plurality ofgears.
 9. The drive device according to claim 1, wherein the pluralityof gears include a motor gear of the drive motor and a mating gearmeshing with the motor gear, and wherein the mating gear includes aninternal gear.
 10. The drive device according to claim 9, furthercomprising a reinforcing projection mounted on the internal gear. 11.The drive device according to claim 9, wherein the internal gear hasinternal helical teeth arranged such that one side far from the drivemotor is disposed downstream from an opposite side near the drive motorin a direction of rotation of the motor gear.
 12. The drive deviceaccording to claim 9, wherein the internal gear includes a cylindricalportion that includes internal teeth mounted on an inner circumferentialsurface and a drive transmitter mounted on an outer circumferentialsurface.
 13. The drive device according to claim 1, wherein the twogears coaxially disposed are integrally formed in a single body andinclude respective helical gears having different twist directions fromeach other.
 14. The drive device according to claim 1, furthercomprising a sound absorber to absorb a sound having a gear meshfrequency of each of the plurality of meshing portions.
 15. The drivedevice according to claim 14, wherein the sound absorber includes aresonator including: a resonance space to acoustically resonate with asound at a predetermined resonant frequency; and a resonance pathcommunicating with the resonance space to guide the sound from anoutside of the resonance space to an inside of the resonance space. 16.The drive device according to claim 1, wherein the drive motor transmitsa driving force to a drive transmission object, and wherein the drivetransmission object is a developing roller.
 17. The drive deviceaccording to claim 1, wherein the drive motor transmits a driving forceto a drive transmission object, and wherein the drive transmissionobject is a photoconductor.
 18. An image forming apparatus comprising:the drive device according to claim 1; and an image forming device toreceive a driving force transmitted from the drive device.